Polyurethanes are a representative general-purpose polymer used for housing and building materials, automobile parts, coating materials, and the like. Polyurethanes are produced by reacting a polyfunctional isocyanate with a polyfunctional alcohol. Isocyanates are obtained by thermally decomposing a carbamic acid ester. As a synthesis method of a carbamic acid ester, a method including reacting an amine, carbon dioxide, and a tin alkoxide compound is known (Patent Literature 1).
According to the method described in Patent Literature 1, a carbamic acid ester can be synthesized with a high yield and high selectivity. Further, the tin alkoxide compound having been used in the reaction can be reused. Therefore, the production method of a carbamic acid ester described in Patent Literature 1 is excellent. However, since a tin alkoxide compound is highly toxic and expensive, the advent of a synthesis method of a carbamic acid ester using a less expensive substance is desired.